Comparisons of Earth system model representation of carbon stored in vegetation with observations

What is it about?

Earth system models (ESMs) have been widely used for projecting global vegetation carbon dynamics, yet how well ESMs performed remains untested. We used observational data to evaluate nine ESMs. ESMs performed well in simulating the spatial distribution of carbon densities in root and total vegetation biomass. However, ESMs performed poorly in simulating absolute carbon densities in root and total vegetation biomass across the majority of land ecosystems, especially in tropical and arctic ecosystems. Particularly, ESMs significantly overestimated carbon density in root and total vegetation biomass in climate zones of 10°S–10°N. Substantial discrepancies between modeled and observed root:total vegetation ratios were found: the root:total vegetation ratios from ESMs were relatively constant, approximately 0.2 across all ecosystems, along latitudinal gradients, and in tropic, temperate, and arctic climatic zones, which was significantly different from the observed large variations in the root:total vegetation ratios (0.1–0.8). The findings in this study indicate an urgent need for model improvements regarding carbon allocation algorithms and more intensive field campaigns targeting carbon density in all key vegetation components.

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